I do my best not to shoot snakes, but would not take a chance if I felt there was danger. In every case so far, I encountered only one at a time, so I just walked away. Closest I ever came was less than one meter before I heard a rattle. I just kep' on moovin'!

I did see a friend hit a rattler with a .44-mag shot shell he loaded himself. I have no memory of what the load was, only that at a distance of about 1.5 meters it blew the snake's head off.
I suspect that like a lot of other things, the load makes a difference.